I don't expect users of an App like SimpleEdit to need to have the very basics of working with a Mac App explained to them. If it turns out I'm wrong - please use the Free and Write manuals for that part. There you will also find information regarding opening documents from iCloud.
The general idea of SimpleEdit is that it can be operated completely by keyboard and that it does not hinder in doing so. That's why you can directly select the definition the moment you create a new document and all that information (like definition, encoding and even the Base URL for the web preview) will be restored, if you have the Auto Save and Resume feature enabled.
Of course, you can disable this feature and SimpleEdit will always start with your default definition. You can change the definition, the encoding and the line ending at any time.
How to edit and change the default definition is described here.
Also depending on the selected definition, you can navigate by keyboard thru your code and select the next or previous symbol/function.
How to show the navigation menu
> Menu > View > Symbols (or Functions)
How to navigate to a symbol/function
Type line number and press return
How to navigate to the previous symbol/function
> Menu > Edit > Previous Symbol (or Function)
How to navigate to the next symbol/function
> Menu > Edit > Next Symbol (or Function)
Probably the best thing about SimpleEdit is its customizable command menu. You can create your own for every definition you use and it does not make use of any sub menus - so you really can use it just by keyboard and you can add your own shortcuts for every menu item. No matter if it is just a snippet, a template, a simple link, a script or even your own command line commands and your own URL requests. How to edit and change those commands is described here.
How to access the command menu
Menu > View > Commands